About the weather station

In March, 1989, the College of Agriculture and the California Irrigation Management Information System (CIMIS) established a weather station for monitoring the variables needed to manage the efficient use of irrigation water. We are Station 78 in a statewide network of 139 active stations. In the summer of 2011, we began retrieving data from the station for use on the Cal Poly Pomona website.

Vapor Pressure: The component of air pressure that is caused by water vapor.

Sunlight: Technically "insolation", the amount of energy from sunlight that is currently hitting the surface of the earth.

Precipitation: The amount of rainfall during 60 seconds at the last reading, expressed as whether it is raining or not.

About precipitation

There are three things most people want to know about precipitation: What form is it in, how hard is it coming down, and how much of it has there been lately. For Cal Poly Pomona, the answer to the first question is almost always "rain"; we have had snow and hail, but they are both exceedingly rare.

The weather station records the second item directly: every minute, it records the amount of precipitation during the previous sixty seconds. We currently express that as "yes" or "no" in answer to the question, "Is it raining?" Eventually we will be able to tell you how hard it's raining, by comparing the value with some benchmarks.

Because we take a reading every five minutes, but the reading covers only one minute of rainfall, we can't add up the numbers to get cumulative precipitation. The weather station accumulates the amount, and that information is retrieved by CIMIS, but not currently by us. Please see the next section for information on how to retrieve it.

Credits

The Cal Poly Pomona Weather Station is a cooperative venture of the College of Agriculture (and especially the Plant Science Department), the Division of Instructional & Information Technology, the Office of Public Affairs, and the California Irrigation Management Information System.